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Abstract:

An electrostatic atomizer equipped with an electrostatic atomization pole
having superior migration-proof. The atomizer comprises the electrostatic
atomization pole, a liquid supply mechanism that supplies the pole with
liquid, and a power supply that supplies the pole with high voltage to
electrostatically atomize the liquid held on the pole. A coating is
formed on the surface of the pole, and the coating is formed of simple
metal or alloy, which displays resistance to migration.

Claims:

1-18. (canceled)

19. An electrostatic atomizer, comprising: an electrostatic atomization
pole comprising an electrode; a liquid supply means for supplying
supplies the pole with liquid; and a voltage supply means for supplying
the pole with high voltage to electrostatically atomize the liquid held
on the pole, wherein a coating is formed on the surface of the pole, said
coating being formed of simple metal or alloy, which displays resistance
to migration, and wherein the pole is a nozzle having at least one hole
at its tip, and the liquid supply means supplies the liquid into the
nozzle.

20. The electrostatic atomizer of claim 19, wherein the resistance of the
coating is superior to that of the pole.

21. The electrostatic atomizer of claim 19, wherein the pole is formed of
Cu or Cu alloy; and the coating is formed of Ni or Ni alloy.

22. The electrostatic atomizer of claim 20, wherein the pole is formed of
Cu or Cu alloy; and the coating is formed of Ni or Ni alloy.

23. The electrostatic atomizer of claim 19, wherein the simple metal or
the alloy forming the coating further displays resistance to acid and
alkali.

24. The electrostatic atomizer of claim 20, wherein the simple metal or
the alloy forming the coating further displays resistance to acid and
alkali.

25. The electrostatic atomizer of claim 23, wherein the simple metal or
the alloy forming the coating is Au, Pd, Pt or Cr, or alloy containing
Au, Pd, Pt or Cr as fundamental material, respectively.

26. The electrostatic atomizer of claim 24, wherein the simple metal or
the alloy forming the coating is Au, Pd, Pt or Cr, or alloy containing
Au, Pd, Pt or Cr as fundamental material, respectively.

27. The electrostatic atomizer of claim 19, wherein the coating further
has high wettability.

28. The electrostatic atomizer of claim 19, wherein thickness of the
coating on the tip region of the pole is thicker than that on the
remaining region of the pole.

29. The electrostatic atomizer of claim 28, wherein thickness of the
coating on the tip region of the pole is thicker than that on the
remaining region of the pole.

Description:

TECHNICAL FIELD

[0001] The invention relates generally to electrostatic atomizers and more
particularly to an electrostatic atomizer that employs electrostatic
atomization of water to generate mist of charged fine particles in the
order of nanometer in size.

BACKGROUND ART

[0002] Such sort of electrostatic atomizer is seen in, for example, the
patent document of Japanese Patent Number 3260150 (European Patent
Publication Number 0 486 198 A1 or U.S. Pat. No. 5,337,963). A prior art
device described in the document comprises a cartridge for storage of
liquid suitable for electrostatic spraying, and a high voltage means for
applying electrostatic potential to the liquid. The cartridge includes a
capillary structure that extends into the interior of the cartridge so as
to feed liquid by capillary action from the cartridge to a spraying
outlet at a tip of the capillary structure. The cartridge also includes a
means for providing an electrically conductive path to allow the
application of an electrostatic charge to the liquid. When the high
voltage means applies the potential to the liquid at the mouth of the
spraying outlet, a potential gradient is developed between innermost and
outermost peripheral surfaces of the mouth, and draws the liquid across
an end face of the spraying outlet towards the outermost peripheral
surface. Thereby, the liquid is projected electrostatically as an array
of ligaments which form a halo around the mouth. In another
configuration, the device is further provided with an electrode connected
to a low potential such as earth.

[0003] However, since the high voltage means applies electrostatic
potential within the range from 10 kV to 25 kV to an electrical contact
in the cartridge, there is an issue that (stress) migration occurs at the
electrical contact.

DISCLOSURE OF THE INVENTION

[0004] It is therefore an object of the present invention to improve
migration-proof of an electrostatic atomization pole that is an
electrode.

[0005] An electrostatic atomizer of the present invention comprises: an
electrostatic atomization pole that is an electrode; a liquid supply
means that supplies the pole with liquid; and a voltage supply means that
supplies the pole with high voltage to electrostatically atomize the
liquid held on the pole. According to one aspect of the invention, a
coating formed on the surface of the pole is provided. The coating is
formed of simple metal or alloy, which displays resistance to migration.
Preferably, the resistance is superior to that of the pole. Thus, the
coating is formed on the surface of the pole and thereby the
migration-proof of the electrostatic atomization pole can be improved. As
a result, electrostatic atomizers having superior durability (long
lifetime) can be provided.

[0006] The pole may be a plug formed of simple metal or alloy having high
thermal conductivity and high electrical conductivity. In this case, the
liquid supply means cools the plug to supply the plug with water as the
liquid through dew formation on the surface of the plug. According to
this configuration, since a means for storage of the liquid is omitted, a
compact electrostatic atomizer can be provided.

[0007] The pole may be a nozzle having at least one hole at its tip. In
this case, the liquid supply means supplies the liquid into the nozzle.
According to this configuration, electrostatic atomization of desired
liquid is possible.

[0008] Preferably, the pole is formed of Cu or Cu alloy, and the coating
is formed of Ni or Ni alloy. According to this structure, the
migration-proof of the electrostatic atomization pole can be improved.
Also in case that the pole is the plug, the plug has superior thermal
conductivity and therefore water can be secured through dew formation and
cost reduction is possible.

[0009] It is also preferable that the simple metal or the alloy forming
the coating further displays resistance to acid and alkali. According to
this structure, acidproof and alkaliproof of the electrostatic
atomization pole can be improved.

[0010] Preferably, the simple metal or the alloy forming the coating is
Au, Pd, Pt or Cr, or alloy containing Au, Pd, Pt or Cr as fundamental
material, respectively. According to this structure, it is possible to
improve migration-proof, wearproof, acidproof and alkaliproof of the
electrostatic atomization pole.

[0011] It is preferable that the coating further has high wettability.
According to this configuration, formation of a Taylor cone becomes easy.

[0012] Preferably, thickness of the coating on the tip region of the pole
is thicker than that on the remaining region of the pole. According to
this structure, it is possible to improve migration-proof in the tip
region where migration is liable to generate.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Preferred embodiments of the invention will now be described in
further details. Other features and advantages of the present invention
will become better understood with regard to the following detailed
description and accompanying drawings where:

[0014] FIG. 1A is a sectional view of a first embodiment according to the
present invention;

[0020] FIG. 5A is a sectional view of a second embodiment according to the
present invention;

[0021]FIG. 5B is a sectional view of the tip of a nozzle in FIG. 5A; and

[0022] FIG. 6 is a sectional view of the tip of a plug in a third
embodiment according to the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

[0023] FIG. 1A is a sectional view of a first embodiment according to the
present invention (i.e., an electrostatic atomizer 1), and FIG. 1B is a
sectional view of the tip of a plug provided for the atomizer 1. The
atomizer 1 comprises a housing 11, an electrostatic atomization pole 12,
a counter electrode 13, a liquid supply mechanism 14, a radiator 15 and a
power supply 16.

[0024] The housing 11 is formed of, for example, insulation material, and
has a cavity 110. The electrostatic atomization pole 12 is a T-shaped
electrode plug having a teardrop-shaped tip 121, and is inserted into and
fixed at a hole of the bottom in the cavity 110 with the tip 121 forward
along an axial direction of the cavity 110. The counter electrode 13 is
located on the opening of the cavity 110 in front of the pole 12.

[0025] The liquid supply mechanism 14 is a Peltier device with a cooling
portion 141 and a heat-radiating portion 142. The portions 141 and 142
are thermally connected to the base end of the electrostatic atomization
pole 12 and the base end of the radiator 15, respectively. The device
cools the electrostatic atomization pole 12 through the cooling portion
141 to supply the pole 12 with water as the liquid through dew formation
on the surface of the pole 12. That is, moisture in the air is supplied
as the water to the surface of the tip 121 of the pole 12.

[0026] The radiator 15 is, for example, a heat-radiating fin, and is
attached to the back of the housing 11 to be thermally connected to the
liquid supply mechanism 14 (heat-radiating portion 142).

[0027] The power supply 16 is a high voltage generator, and applies high
voltage across the pole 12 and the electrode 13 to electrostatically
atomize the liquid held on the pole 12. A positive output terminal of the
generator is connected to Ground and the electrode 13, while its negative
output terminal is connected to the pole 12. When the high voltage is
applied across the pole 12 and the electrode 13, a negative electronic
charge concentrates on the pole 12 (negative electrode), and also water
held on the tip 121 of the pole 12 rises like a cone to form a Taylor
cone. When the negative electronic charge concentrates on the tip of the
Taylor cone to become high density, repulsion in the high density of the
electronic charge brings about Rayleigh splitting to split and scatter
the Taylor cone shaped water. The power supply 16 repeats the Rayleigh
splitting to realize electrostatic atomization.

[0028] As mentioned above, if the electrostatic atomization pole 12
holding the liquid on the surface of the tip 121 is repeatedly subjected
to the high voltage over a long period, the pole 12 has a tendency to be
transformed from a normal shape as shown in FIG. 2A into another shape as
shown in FIG. 2B through migration. Thus, if the normal shape is
transformed, the above Taylor cone is not normally formed and therefore
the electrostatic atomizer 1 can not normally operate.

[0029] Then, according to an aspect of the first embodiment, as shown in
FIG. 1B, a coating 10 formed on the surface of the electrostatic
atomization pole 12 is provided. First, the pole 12 itself is formed by
cutting of Cu--Sn (brass material) with high thermal conductivity and
high electrical conductivity. Thereby, the pole 12 can be cooled
efficiently and also the pole 12 can be easily discharged. But the
material of the pole 12 is not limited to the brass material, the
material may be simple metal (e.g., Cu or the like) or alloy (e.g., Cu
alloy except the brass material, or the like), having high thermal
conductivity and high electrical conductivity.

[0030] After surface treatment of the electrostatic atomization pole 12,
the coating 10 is formed on the surface of the pole 12. The coating 10 is
formed of simple metal or alloy, which displays resistance to migration.
The coating 10 in the first embodiment is a Ni plating layer having
migration-proof that is superior to the brass material. For example, in
case of non-electrolytic plating, the thickness of the coating 10 can be
formed to the uniform thickness as shown in FIG. 1B. In order to prevent
formation of pinhole defects, the thickness of the coating 10 is
preferably equal to or more than 4 μm and more preferably about 20
μm including a margin. Incidentally, it is preferable to secure high
wettability of the surface. Because wettability of the surface of the
whole pole 12 including the coating 10 influences formation of the Taylor
cone and low wettability prevents formation of appropriate Taylor cone to
reduce electrostatic atomization efficiency.

[0031] Thus, by forming the coating 10 on the surface of the electrostatic
atomization pole 12, the migration-proof of the pole 12 can be improved.
Consequently, the electrostatic atomizer 1 having superior durability
(long lifetime) can be provided.

[0032] In a modified embodiment, as shown in FIG. 3, the coating 10 is a
Ni plating layer by electrolytic plating. This sort of layer has a
tendency to become thicker in sharp part in general. Therefore, by
employing the tendency, thickness T of the coating 10 on the top of the
tip 121 can be made thicker than thickness T' of the coating 10 on the
other part. Accordingly, the thicker part of the coating 10 can
preferably protect the top of the tip 121 where migration can easily
occur. Also in case of the electrolytic plating, the production cost can
be held down and productivity can be improved. But not limited to this,
as shown in FIG. 4, the coating 10 may be formed only on the top of the
tip 121 where migration easily occurs and also Taylor cone is formed.

[0033] In another modified embodiment, the electrostatic atomizer 1 does
not comprise the counter electrode 13, and the power supply 16 supplies
the electrostatic atomization pole 12 with high voltage with respect to
ground potential.

[0034] FIG. 5A is a sectional view of a second embodiment according to the
present invention (i.e., an electrostatic atomizer 2), and FIG. 5B is a
sectional view of the tip of a nozzle provided for the atomizer 2. The
atomizer 2 comprises a housing 21, an electrostatic atomization pole 22,
a counter electrode 23, a liquid supply mechanism 24 and a power supply
26.

[0035] The housing 21 is formed of, for example, insulation material, and
has a cavity 210. The electrostatic atomization pole 22 is an arch-shaped
hollow electrode nozzle having holes (221a, . . . ) at its tip 221, and
is inserted into and fixed at a hole of the bottom in the cavity 210 with
the tip 221 forward along an axial direction of the cavity 210. The
counter electrode 23 is located on the opening of the cavity 210 in front
of the pole 22.

[0036] The liquid supply mechanism 24 is formed of a liquid storage
portion 241 for storing liquid (e.g., water W) and a liquid supply
portion 242 for supplying the liquid into the pole 22. For example, the
liquid supply portion 242 has capillary tubes (242a, . . . ) that
transport liquid by capillary action, and transports the liquid in the
portion 241 to the inner surface of the tip 221 of the pole 22 through
the capillary tubes as well as a gap 242b between the pole 22 and the
portion 242. However, not limited to this, the liquid supply portion 242
may be formed of porous material having pores for transporting liquid by
capillary action.

[0037] The power supply 26 is a high voltage generator, and applies high
voltage across the pole 22 and the electrode 23 to electrostatically
atomize the liquid held on the pole 22 like the power supply 16 of the
first embodiment. In the second embodiment, the liquid transported to the
inner surface of the tip 221 moves to the outer surface of the tip 221
via the holes (221a, . . . ) and then is atomized electrostatically.

[0038] According to an aspect of the second embodiment, as shown in FIG.
5B, a coating 20 formed on the surface of the electrostatic atomization
pole 22 is provided. The pole 22 itself is formed of, for example, SUS or
the like, while the coating 20 is formed of metal (e.g., Ni or Ni alloy)
having migration-proof that is superior to the pole 22. However, not
limited to this, the coating 20 may be further formed on the inner
surface of the pole 22 and/or the inner periphery of each hole 221a.

[0039] Thus, by forming the coating 20 on the surface of the electrostatic
atomization pole 22, the migration-proof of the pole 22 can be improved.
Consequently, the electrostatic atomizer 2 having superior durability
(long lifetime) can be provided.

[0040] FIG. 6 is a sectional view of the tip of a plug in a third
embodiment according to the present invention. The third embodiment
comprises' a housing, an electrostatic atomization pole 32, a counter
electrode, a liquid supply mechanism, a radiator and a power supply in
the same way as those of the first embodiment. In addition, according to
an aspect of the third embodiment there is provided a coating 30 that is
formed on the surface of the electrostatic atomization pole 32 and has a
particular structure that is different from those of the first and second
embodiments.

[0041] The coating 30 has a three-layer structure formed by barrel plating
(electroplating) in order to cope with water that is supplied from the
liquid supply mechanism and may be acid or alkali besides neutral.
Specifically, the coating 30 is constructed of a first layer 30a formed
on the surface of the electrostatic atomization pole 32, a second layer
30b formed on the surface of the layer 30a and a third layer 30c formed
on the surface of the layer 30b.

[0042] Though the first layer 30a is a Ni plating layer that is about 15
μm in thickness and displays migration-proof superior to the
electrostatic atomization pole 32, the layer 30a is provided mainly to
prevent Cu contained in the pole 32 and after-mentioned Au contained in
the second and the third layers from diffusing mutually. On account of
this, the thickness of the layer 30a requires at least equal to or more
than 1 μm. Also in order to prevent formation of pinhole defects, the
thickness is preferably equal to or more than 4 μm and more preferably
about 15 μm including a margin.

[0043] The second layer 30b and the third layer 30c are provided mainly to
improve migration-proof, wearproof, acidproof and alkaliproof. That is,
the layer 30b is an Au plating layer that is about 7 μm in thickness,
and the layer 30c is an Au plating layer that is about 3 μn in
thickness and contains added Co. The Au contained in the layers 30b and
30c has superior migration-proof, wearproof, acidproof, alkaliproof and
productivity (barrel plating possible), and raises those characteristics
of the pole 32. In order to prevent formation of pinhole defects, the
thickness of the layer 30b is preferably equal to or more than 4 μm
and more preferably about 7 μm including a margin. The Au plating
layer containing Co, i.e., the layer 30c has high wettability, and also
has hardness raised up to about Hv (Vickers Hardness) 250 from about Hv
80 to protect the layer 30c itself from flaw. Though the coating 30 may
have one Au plating layer that contains added Co instead of the layers
30b and 30c, the upper limit of thickness of the Au plating layer
containing Co is about 3 μm, and therefore the coating 30 of the third
embodiment will have the layer 30b without Co and gloss and the layer 30c
with Co and gloss in addition to the layer 30a. Thereby, thickness of the
part of the Au plating layers can be increased.

[0044] A result of comparison test (continuous operation test) between a
sample 1' corresponding to the electrostatic atomization pole 12 and a
sample 3' corresponding to the electrostatic atomization pole 32 is now
explained. The coating of the sample 1' consisted of only a Ni plating
layer, and this layer was about 19 μm in thickness. The coating of the
sample 3' consisted of a Ni plating layer that was about 1 μm in
thickness, and an Au plating layer that was about 18 μm in thickness
and did not contain Co. However, the coating of the sample 3' was not
provided with a layer corresponding to the third layer 30c.

[0045] An electrostatic atomizer as shown in FIG. 1A was equipped with
each of the samples 1' and 3' one after another, and each sample was
continuously driven through the atomizer for about 100 hours. Then,
deterioration degree of each sample was measured, and the result of
continuous operation test was obtained. In the result, deterioration was
not detected from the sample 3', whereas deterioration (wear) was
detected from the sample 1'. That is, the thickness of the Ni plating
layer of the sample 1' decreased from about 19 μm to about 12 μm.
From the result, it is understood that the Au plating layer has high
migration proof and high wearproof. On the other hand, the Ni plating
layer was able to prevent migration, but was not able to prevent the
wear. The Ni plating layer has hardness about Hv 500 harder than hardness
about Hv 80 of the Au plating layer, while the Ni plating layer has
wearproof and acidproof that are inferior to the Au plating layer.
Therefore, it is thought that the above deterioration of the sample 1'
could not be caused by dynamic contact, friction and so on, and was wear
caused by chemical corrosion.

[0046] Next, a result of acid resistance test for the sample 3' is
explained. After the sample 3' was soaked in a solution of 10%
H2SO4 at 95° for 10 hours, corrosion degree of the
sample 3' was measured. In the result of this test, corrosion was not
detected from the sample 3'.

[0047] Next, a result of alkali resistance test for the sample 3' is
explained. After the sample 3' was soaked in a solution of 10% NaOH at
95° for 10 hours, corrosion degree of the sample 3' was measured.
In the result of this test, corrosion was not detected from the sample
3'.

[0048] From each result of the above tests, it is understood that
migration-proof, wearproof, acidproof and alkaliproof of an electrostatic
atomization pole can be improved by adding a coating containing an Au
plating layer to the pole. Therefore, it is possible to improve not only
the migration-proof of an electrostatic atomization pole but also its
wearproof, acidproof and alkaliproof by forming a coating including at
least one such second layer in addition to such a first layer on the
surface of the pole. As a result, electrostatic atomizers having more
superior durability (long lifetime) can be provided. Also in case of the
barrel plating, electrostatic atomizers with the coatings can be
mass-produced at a low price and therefore the productivity is improved.
Incidentally, the coating can be also applied to that of the second
embodiment.

[0049] In the third embodiment, Au is employed in order to improve
migration-proof, wearproof, acidproof and alkaliproof, but the coating of
the present invention is not limited to Au and may include a layer formed
of simple metal of, for example, Pd, Pt or Cr, or include a layer formed
of, for example, Pd, Pt or Cr alloy. Also in this case, advantages
similar to the third embodiment are obtained.

[0050] Although the present invention has been described with reference to
certain preferred embodiments, numerous modifications and variations can
be made by those skilled in the art without departing from the true
spirit and scope of this invention.